Prematurity, enteral formula feeding, and bacterial colonization are three major risk factors for neonatal necrotizing enterocolitis (NEC). The hallmark pathologic findings in NEC are intestinal mucosal injuries. However, the etiology and pathogenesis of NEC remain unclear. Acetic acid, propionic acid and butyric acid are short chain fatty acids (SCFAs) which are produced mainly in the colon by bacterial fermentation of undigested carbohydrates. In physiological condition, the production of SCFAs in the bowel is very important for energy salvage and crucial for gastrointestinal adaptation and maturation. However, excessive concentrations of SCFAs (especially butyrate) can deregulate the normal process of apoptosis and may cause disruption of the intestinal barrier. Once the intestinal barrier is disrupted, the inflammatory cascade may be activated, which can induce further injury to the intestinal mucosa. Therefore overproduction/accumulation of SCFAs in the intestinal lumen may play a pivotal role in the pathogenesis of NEC. Our previous study and our preliminary data suggest that butyrate in physiological concentration promotes the intestinal barrier function by regulating the assembly of tight junctions via activating AMP-activated protein kinase (AMPK). Excessive luminal SCFAs, especially butyrate, however may induce severe apoptosis and disrupting mucosal barrier. The overall objectives of this proposal are to elucidate the molecular mechanisms underlying the effects of butyrate on intestinal barrier function. Firstly, we will determine if AMPK activation is the primary mechanism mediating the effect of butyrate at physiological concentration on the assembly of tight junction proteins by using a well established Caco-2 cell monolayer model. Then, by using the same Caco-2 cell monolayer model, we will determine if the augmented apoptosis induced by butyrate explains the detrimental effect of excessive butyrate on the intestinal barrier. PUBLIC HEALTH RELEVANCE: Short chain fatty acids (SCFAs) in physiological concentration promote the intestinal barrier function. However, excessive luminal SCFAs, especially butyrate, can cause intestinal injury by inducing severe apoptosis and disrupting mucosal barrier function. The project of this proposal is to further elucidate the molecular mechanisms underlying the effects of butyrate on intestinal barrier function, which may help us understand the role of SCFAs in the pathogenesis of neonatal necrotizing enterocolitis (NEC).